Art of cracking hydrocarbons



Feb. 16, 1932. PELZER 1,845,554

ART OF CRACKING HYDROCARBONS Filed April 4, 1930 INVENTOR Adar/ L. (e/zer- BY 62m! ORNEYS Patented Feb. 16, 1932 UNITED STATES PATENT orrlcs HARRY L. PELZEB, F HOUSTON, TEXAS, ASSIGNOR TO SINCLAIR DEFINING- COEPANY,

OF NEW YORK, N. Y., A CORPORATION OF MAINE ART OF CRACKING HYDROCABBONS Application filed April 4, 1980. Serial No. 441,648.

' ing hydrocarbon oils, such as gas oil and reduced crude oil, by cracking operations. This invention provides improvements, in both methods and apparatus for heating oil to cracking temperatures, which are advantageous in several respects but particularly in that they afiord methods and'apparatus by which the temperature gradient of the oil passing thru the heating operation may be given almost any desired characteristics;

at the choice of the operator, both effectively and efliciently.

The development of cracking operations in which oil is subjected to severe cracking conditions to produce motor fuel gasoline of improved anti-knock properties has developed, as an element of increasing importance, a requirement for more precise control of the temperature gradient of the oil passing thru the heating operation and for the maintenance of temperature gradients having characteristics not to be obtained by the more simple heater arrangements and heating operations previously used. This invention is of general application in meeting these requirements in conjunction with various types of cracking 0 eration.

This invention, however, is of special value and application in carrying out operations in which high boiling oil is heated to a cracking temperature under high pressure and in which the hot oil products of this heatin operation are separated into a vaporized Traction and an unvaporized fraction under lower pressure, or so-called pressure coil cracking operations. This invention is also of value and application in carrying out operations in which'high boiling oil 1s heated to a high cracking temperature substantially in the vapor phase.

In its broad aspect, this invention comprises the reheating of heating gases which have passed over the heating tubes in which the oil is heated to a cracking temperature by heat exchange with heating gases fresh from he fire-box. from which the heating gases are initially supplied, before the latter first contact with the heating tubes and the recirculation of the thus reheated heating gases over the heating tubes, or part of the heating tubes, together with the heating gases passing over the heating tubes from the fire-box. The heat exchange may be either direct or indirect. In its specific aspect, this invention involves more particularly the indirect heat exchange. The modification of this invention involving more particularly the direct heat exchange is described in more detail in my application filed April 4, 1930, Serial No. 441,649.

In carr ing out the method of this invention, heating ses from a fire-box in which fuel is burn are passed successivel over a first battery and a second battery 0 heating tubes, a part of the heating gases which have passed over both batteries of heating tubes is passed in indirect heat exchanging relation with the heating gases from the firebox before the latter heating gases pass over the first battery of heating tubes, the thus reheated heating ases are passed over the second battery of eating tubes together with the heating gases which have passed over the first battery of heating tubes, and oil is passed thru one and then the other of the batteries of heating tubes and heated to a cracking temperature during passage therethru. The heat exchange between the recirculated heating gases and the heating gases fresh from the fire-box may be carried out so that radiant heat from the fire-box is absorbed in the recirculated heating ases. The heating gases fresh from the re-box are thus tempered at the same time that the recirculated heating gases are heated. The heating tubes may be subdivided into more than two batteries and the reheated recirculated heating gases introduced at a plurality of points during the passage of the heating gases over the several batteries of heating tubes.

Thus, according to the invention, almost any desired temperature gradient may be maintained with respect to the oil passing with the heating tubes, and the thus Heated recirculated heating gases may be utilized to reheat, by admixture therewith, the heating gases passing over the heating tubes at one or more points during their passage thereover, to temperatures as high as or higher than that at which the heating gases first contact with the heating tubes. The extremely flexible control of the temperature gradient of the heating gases during their passage over the heating tubes thus afforded makes possible, in conjunction with control of the rate of oil circulation and the direction of oil circulation thru the heater, the maintenance of almost any desired temperature gradient of the oil passing thru the heater.

The oil may be passed thru the batteries of heating tubes generally countercurrent to the flow of heating gases thereover or generally concurrent with the flow of heating gases thereover, or the oil may be passed in part countercurrent to and in part concurrent with the flow of heating gases over the heating tubes. One of the advantages of the invention, however, is that it makes possible elimination of inversions and reinversions of the direction of oil flow in passage thru the heater without sacrifice with respect to flexibility of control. Thus, according to the inventlon, almost any desired temperature gradient of the oil passing thru the heater may be maintained with simple continuous flow of the oil thru the heater, either generally countercurrent to or generally concurrent with the flow of heating gases.

- According to the invention, oil flowing thru the heater may be brought rapidly to a high cracking temperature and then maintained at substantiall the same temperature for a further period 1n the heater. or it may be brought rapidly to a hi h cracking temperature and then maintaine at a temperature increasing at a slower rate and approximately uniformly with respect to time for a further period in the heater, or it may be heated to a temperature ultimately a cracking temperature, progressively increasing but increasing at a diminishing rate while flowing thru the heater, for example.

The apparatus of the invention comprises a heating flue and heating tubes arranged in the heating flue, a fire-box communicating thru a heat exchanger with one end of the heating flue, means for forcing heating gases withdrawn from the other end of the heating flue thru the heat exchanger and into the heating flue at an intermediate point, and means for forcing oil thru the heating tubes. The heat exchanger is advantageously arranged to absorb radiant heat from the fire-box.

The invention will be further described in connection with the accompanying drawings which illustrate, diagrammatically and conventionally, in elevation and partly in section and with parts broken away, three forms of apparatus, shown severally in Figs. 1, 2 and 3, embodying the invention and adapted for carrying out the invention. The same parts in the several figures are designated by the same reference character.

Referring to the drawings, the apparatus illustrated comprises a furnace including a fire-box 4- and a heating flue 5, a fine 6 connecting the fire-box 4 with the upper end of the heating flue 5 and a stack flue 7 communicating with the lower end of the heating flue 5, a heatexchanger arranged in the flue 6, and ducts 8 and 9 including a fan 10 adapted to withdraw heating gases from the lower end of the heating flue 5 pass them through the heat exchanger and then thru the lower part of the heating flue 5. The heat exchanger is designated 11 in Fig. 1, 11a in Fig. 2 and 11?) and 110 in Fig. 3. Two or more batteries of heating tubes, connected in series to form a continuous heating conduit, are arranged in the heating flue 5 and a pump 12 is provided for forcing oil thru the heating tubes. The oil is supplied to the heating tubes thru the connection 13 in Figs.

' 1 and 2, thru the connection 14 in Fig. 3, and

the hot oil products are discharged from the heating tubes thru the connection 15 in Figs. 1 and 2, thru connection 16 in Fig. 3. In carrying out so-called pressure coil cracking operations in the apparatus illustrated, the pressure in the heater may be maintained and regulated by means of the valve 17, and

an oil cooler than the hot oil products dis- 1 charged thru the connection 15 or 16 may be introduced thru the connection 18 to arrest the cracking reaction initiated in the heater. The hot oil products may be discharged thru connection 19, in the case of so-called pressure coil cracking operations for example, to any suitable evaporator for the separation of vaporized and unvaporized fractions or, in the case of vapor phase cracking operations, to a tar separator.

The heat exchanges 11, 11a, 11b and 110, may consist of one or more tile ducts arranged within the flue 6 and connected to the duct 9 at one end and to the heating flue 5 at the other end. These heat exchanges may, with advantage, be positioned, as illustrated, to absorb radiant heat from the fire-box 4 as well as sensible heat from the heating gases from the fire-box. By arranging the heat exchanger as illustrated in Fig. '2, to-provide generally countercurrent flow between the recirculated heating gases and the heating gases fresh from the fire-box, the reheated recirculated heating gases may be brought to a higher temperature than in a transverse flow heat exchanger as in the apparatus illustrated in Figs; 1 and 3.

The apparatus illustrated in Figs. 1 and 2 comprises two batteries of heating tubes, 20 and 21, Itwill be understood that the illustration of the arrangement of the heating tubes is diagrammatic and conventional merely. In the apparatus illustrated in both Figs. 1 and 2, the recirculated heating gases reheated in the heat exchanger 11 or 11a are introduced into the heating flue 5 at a point intermediate the two batteries of heating tubes 20 and 21. In the apparatus illustrated in both these figures, the oil is supplied to the battery of heating tubes 21 thru connection 13, passed from the battery 21 to the battery of heating tubes 20 thru the connections 22 and 23, and discharged from the battery 20 thru the connection 15. The oil may likewise be supplied to the battery 20 thru the connection 15, passed from the battery 20 to the battery 21 thru the connections 23 and 22, and discharged from the battery 21 thru the connection 13, or the oil may be supplied to the battery 21 thru the connection 13, passed to the battery 20 thru the connections 22 and 15, and discharged thru the connection 23, the connection 19 then being connected to the connection 23. In the apparatus illustrated in Fig. 3, oil is supplied to the several batteries of heating tubes 24, 25, 26 and 27 thru the connection 16, passed thru the several batteries of heating tubes successively, and discharged from the last thru the connection 14, the recirculated heating gases reheated in each exchanger 116 being introduced into the heating flue 5 intermediate the battery 25 and the battery 26, and those reheated in heat exchanger 110 being introduced into the heating flue 5 intermediate the battery 26 and the battery 27.

That part of the heating gases withdrawn from the lower end of the heating flue 5 and not recirculated thru the lower part of the heating flue 5 is discharged thru the stack (lue 28. Fuel for combustion is supplied to the firebox, in the apparatus illustrated. by means of the burner 29. Air supplied to the fire-box 4 for combustion may be preheated. as in the apparatus illustrated in Figs. 1 and 3, by heat exchange with the escaping waste heating gases.

Dampers are provided, as illustrated, in the stack flue 28 and in the recirculation duct 9, or the branches therefrom 30, 31,. and 32, for controlling, in coniunction with regulation of the fan 10, the flow of heating gases therefrom.

In the apparatus in the several figures, the rate of heat transfer in the lower part of the heating flue 5 is improved because of the increased velocity of flow of heating gases therethru resulting from the increase in volume of the heating gases flowing therethru because of the recirculation of the heating gases introduced into the heating flue thru the heat exchanger, or heat exchangers. Altho the heating tubes in the upper part of the heating flue 5 are the first to contact with the heating gases fresh from the fire-box, they contact with these fresh heating gases only after the latter have been tempered because of the heat absorbed therefrom thru the heat exchanger, or heat exchangers, thru which these heating gases pass before they first contact with the heating tubes. The branch duct 32, in the apparatus illustrated in Fig. 3,

viously noted, the arrangement of the heat ex changer 11a makes it possible to reheat the recirculated heating gases to a temperature higher than that of the heating gases fresh from the fire-box as they first contact with the heating tubes of the first battery 20, this in turn making it possible to bring the heating gases which have passed over the first battery of heating tubes 20 before they pass over the second battery of heating tubes 21 to a temperature as high or higher than that of the heating gases fresh from the fire-box as they first contact with the heating tubes of the first battery 20. By passing the oil first thru the second battery of heating tubes 21 and then thru the first battery of heating tubes 20 in the apparatus illustrated in Fig 2, the oil may be brought rapidly to a high cracking temperature and then, according to the rate of oil circulation, the rate of firing and the rate of recirculation of heating gases, maintained at that temperature or at a temperature progressively increasing therefrom at a controllable rate. It Will be apparent that this embodiment of the invention enjoys all of the advantages of countercurrent heat exchange between the heating gases and the oil flowing thru the heater without, however, being subject to the limitations with respect to the temperature gradient of the oil flowing thru the heater usually involved in the maintenance of this simple countercurrent relation.

Further control of the temperature gradisome cases, the flexibility afforded by the apparatus illustrated in Figs. 1 and 2 is sufficient for usual purposes. It will be understood that provision for recirculation of heating gases thruout the heating flue may be combined with provision for introduction of reheated recirculated hcatinggases into the heating flue at one intermediate point, as in the apparatus illustrated in Figs. 1 and 2, or at more than two intermediate points.

I claim:

1. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, passing a part of the heating gases which have passed over both batteries of heating tubes in indirect-heat exchanging relation with the heating gases from the firebox before the latter heating gases pass over the first battery of heating tubes, introducing thus reheated heating gases into the heating gases passing from the fire-box successively over the first and second battery of heating tubes at a point intermediate their passage over the first and second battery of heating tubes, passing the thus reheated heat-ing gases over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes and passing oil thru one of the batteries of heating tubes and then thru the other and heating it to a cracking temperature during passage therethru.

2. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successive- 1y over a first battery and a second battery of heating tubes, passing a part of the heating gases which have passed over both batteries of heating tubes in indirect heat exchanging relation with the heating gases from the fire-box before the latter heating gases pass over the first battery of heating tubes, introducing thus reheated heating gases into the heating gases passing from the fire-box successively over the first and sec-- ond battery of heating tubes at a point intermediate their passage over the first and second battery of heating tubes, passing the thus reheated heating gases over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes, and passing oil first thru the second battery of heating tubes and then thru the first and heating it to a clracking temperature during passage theret iru.

3. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, passing a part of the heating gases which have passed over both batteries of heating tubes in indirect heat exchanging relation with the heating gases from the firebox before the latter heating gases pass over the first battery of heating tubes, introducing thus reheated heating gases into the heating gases passing from the fire-box successively over the first and second battery of heating tubes at a point intermediate their passage over the first and second battery of heating tubes, passing the thus reheated heating g ases over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes, and passing oil first thru the first battery of heating tubes and then thru the second and heating it to a cracking temperature during passage therethru.

4. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, said batteries of heating tubes being protected from direct radiation from said fire-box, absorbing radiant heat from said fire box in heating gases, a part of the heating gases which have passed over both batteries of heating tubes, passed in indirect heat exchanging relation with the heating gases from the fire-box before the latter heating gases pass over the first battery of heating tubes, introducing thus reheated heating 'ases into the heating gases passing from the fire-box successively over the first and second battery of heating tubes at a point intermediatetheir passage over the first and second battery of heating tubes, passing the thus reheated heating gases over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes, and passing oil thru one of the batteries of heating tubes and then thru the other and heating it to a cracking temperature during passage therethru.

5. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes while out of contact with the heating gases fresh from the fire-box, subsequently introducing the reheated heating ases into the heating gases passing from the re-box successively over the first and second battery of heating tubes at a point intermediate their passage overthefirst andsecond battery of heating tubes, passing the reheated heating gases over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes, and passing oil thru one of the Leaasee batteries of heating tubes and then thru the other and heating it" to a cracking temperature during passage therethru.

6. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes by indirect heat exchange with the heating gases from the tire-box to a temperature higher than that oi": the heating gases from the fire-box as they first contact with the heating tubes of the first battery, passing the thus reheated heating gases over the second battery of heating tubes together with the heating gases which havepassed over the first battery of heating tubes, and passing oil thru one of the batteries of heating tubes and then thru the other and heating it to a cracking temperature during passage therethru.

7. In heating oil to cracking temperatures in. cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes by indirect heat exchange With the heating gases from the firebox to a temperature higher than that of the heating gases from the fire-box as they first contact with the heating tubes of the first battery, admixing the thus reheated heating gases with the heating gases which have passed over the first battery of heating tubes before the latter pass over the second bati tery of heating tubes and thereby bringing the resulting mixture of heating gases to a temperature higher than that of the heating gases from the tire-box as they first Contact with the heating tubes of the first battery, and pass ng oil thru one of the batteries of heatmg tubes and then thru the other and heating it to a cracking temperature during passage therethru.

8. In heating oil to cracking temperatures in cracking operations. the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a. first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes by indirect heat ex change with the heating gases from the firebox to a temperature higher than that of the heating gases from the fire-box as they first contact a ith the heating tubes oi the first battery, admixing the thus reheated heating gases with the heating gases which have passed over the first battery of heating tubes before the latter pass over the second battery of he ting tubes and thereby bringing the resulting mixture of heating gases to a tem ing ten'iperatures, in combination, a he perature higher than that of the heating from the fire-boa as they first contact with the heating tubes of the first batter and passing oil first thru the second battery of heating tubes and then thru the first and heating it tn m a cracking temperature during passage therethru,

,9. In heatingoil to cracking temperatures in cracking operations, the improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes by indirect heat exchange with the heating gases from the i, box to a temperature not lower than that of the heating gases from the fire-box as they first contact with the heating tubes of the first battery, passing the thus reheated. heatin gases over the second battery lot heating tubes together'with the heating gases which have passed over the first battery of heating tubes, and passing oil thru one of the he teries of heating tubes and then thru' the other and heating it to a cracking tempera ture during passage therethrun 10. In heating oil to cracking temperatures in cracking operations the improvement which comprises passing heating gases from a. firebox in Whici fuel is burned sue cess'ively over a plurality of batteries of heat ing tubes, reheating a part of the heathe gases which have passed over the bait of heating tubes by indirect hes with the heating gases from. the ri her; be fore the latter heating gases pass over the first battery of heating tubes, intrude i the thus reheated heating gases into admin ture with the heating gases passing from the fire-box successively over the batteries (if. heating tubes at a plurality 01" points in such passage of the heating gases over the heating tubes, and passing oil thru the batteries of heating tubes and heating it to'a cracking temperature therein. i 11. In apparatus for heating oil to arachlng temperatures, in combination, a heating flue and heating tubes'arranged therein, a fire-box communicating thru heat er with one end of said heating flue, for forcing heating gases withdrawn from. the other end of said heating iiue thr'a s. i heat exchanger into said heating this point intermediate said heating tubes, c" means for forcing oil thru said he 12. in apparatus for heating 0 fine and heating'tubes arranged the fire box communicating thru er with one end of said he for forcing heating f the other end of said hea (A heat exchanger and into said he a piuraiity of points ing temperatures, in combination,

a ment which comp ing tubes, and means for forcing oil thru said heatin tubes.

13. apparatus for heating oil to crack a heating due and heating tubes arranged therein, a heat exchan er and a fire-box, communicatin theret ru with one end of said heating ue, said heat exchan er being arranged to absorb radiant heat rom said fire-box, means for forcing heating gases withdrawn from the other end of said heating flue thru said heat exchanger-into said heating flue at a point intermediate said heating tubes, and means for forcing oil thru said heating tubes.

14. In heating oil to cracking temperatures in cracking operations, the-improvement which comprises passing heating gases from a fire-box in which fuel is burned successively over a first battery and a second battery of heating tubes, reheating a part of the heatin gases which have passed over both batteries of heating tubes, to a temperature at least as high as that of the heating gases from the fire-boil when they last contact with the heating tubes of the first battery passing the reheated heating gases only over the second battery of heating tubes together with the heating gases which have passed over the first battery of heating tubes and passin oil thru one of the batteries of heating tu es and-then thru the other and first battery of tubes at a plurality of points intermediate their passage between the batteries of heating tubes and passing the said reheated heating gases over subsequent batteries of heating tubes together with the heating gases from the fire-box, recirculating another part of the heating uses which have passed over the batteries 0 heating tubes into. the heating gases passin from the fire box to the eating tubes, passing oil through one of the batteries of heating tubes and then through the others and heating it to a cracking temperature during passage therethrough.

In testimony whereof I aifix my signature.

HARRY- L, PELZER.

heating it to a cracking temperature during passage therethru.

15. In heating oil to cracking temperatures in cracking operations, the improvement which comprises passing heatin gases from a fire-box in which fuel is burne successively over a first battery and a second battery of heating tubes, reheating a part of the heating gases which have passed over both batteries of heating tubes by indirect heat exchange with heating gases from the fire-box before the latter heating gases pass over the first batter of heating tubes, introducing the thus re eated heating gases into admixture with the heating gases passing from the fire-box successively over t e first and second battery of heating tubes at a point intermediate their passage between the first and second battery of heating tubes, passing the said reheated heating gases over the second battery of heating tubes-together with the heating gases which have passed over the first battery of heating tubes, recirculating another part of the heating gases over both batteries 'of heating tubes and passing oil throu h and t en through the other and heating it to a cracking temperature during passage therethrough.

16. In heating oil to cracking temperaone of the batteries of heating tubes tures in cracking operations, the improverises passing heating gases from a fire-box in which fuel is burned suc- 

